The invention relates to a tyre condition monitoring system, to a sensor device, a wheel transmitter unit and a transducer for use therewith, to a method of calibration, and to a transceiver circuit.
Tyre condition monitoring systems are used to monitor the condition of tyres on a vehicle in order to increase the safety and efficiency of the vehicle. There has been a great deal of interest in tyre monitoring in the past and some examples of recent proposals are disclosed in U.S. Pat. No. 4,703,650, U.S. Pat. No. 4,737,761, U.S. Pat. No. 4,823,107, U.S. Pat. No. 4,837,553, U.S. Pat. No. 4,843,872, U.S. Pat. No. 4,893,110, U.S. Pat. No. 5,029,468 and U.S. Pat. No. 5,054,315.
In our International Patent Application No. PCT/GB 93/02005 published as WO-A-94/06640 we describe a tyre condition monitoring system comprising a unit mountable in a wheel of a vehicle. The unit comprises a sensor, a voltage controlled oscillator and a code generator arranged such that a coded signal is generated in a time period related to the value of the pressure or temperature sensed by the sensor. In order to conserve power the unit comprises a power supply which is activated by a timer from time to time causing the coded signal to be transmitted. Once the code has been transmitted the power supply is deactivated. The unit further comprises a monitor circuit which continuously monitors the sensor for an unacceptable pressure or temperature condition. An override circuit is responsive to the monitor circuit or to an external stimulus to activate the power supply.
International Patent Application No. PCT/CA 92/00072 published as WO-A-92/14620 describes a tyre monitoring apparatus and method in which a code representing a measured physical quantity, property or condition of a tyre is transmitted. The circuit is operable in an active mode in which a measurement circuit measures an instantaneous value of temperature and pressure and a transmitter circuit transmits a signal representing the sensed instantaneous values of pressure and temperature. In the low power mode minimal power is consumed by the measurement and transmitter circuits.
The present invention aims to provide among other things an improved tyre condition monitoring system.
According to one aspect of the invention there is provided a sensor device for sensing parameters associated with a pressurised unit, the sensor device comprising a sensor for sending one or more parameters associated with said pressurised unit, a processor for processing signals from the sensor, and a transmitter for transmitting data, the processor being operable in plural different modes including a calibration mode in which data is recorded for known conditions and in a normal operating mode in which data representing the one or more sensed parameters is transmitted by the transmitter.
According to another aspect of the invention there is provided a wheel transmitter unit for a tyre condition monitoring system, the wheel transmitter unit being mountable to a wheel and comprising a sensor for sensing one or more parameters associated with said wheel, a transmitter for transmitting data representing the sensed one or more parameters, a power supply for supplying power to the sensor and the transmitter, and a condition monitor arranged to respond to operating conditions of the wheel transmitter unit to vary the manner in which the transmitter unit transmits data.
According to a further aspect of the invention there is provided a transducer comprising: a pressure sensor for producing an output proportional to pressure applied thereto; a temperature sensor for producing an output representing the temperature thereof; storing means for storing calibration data representing the behaviour of the pressure sensor in response to both pressure and temperature; and processing means for processing the pressure and temperature sensor outputs with reference to the stored calibration data to produce a calibrated output representing directly the pressure applied to the transducer.
In another aspect the invention provides a tyre condition monitoring system, comprising at least one sensor device or wheel transmitter unit mountable in the wheel of a vehicle; and a receiver unit for receiving the data transmitted by the at least one sensor device or wheel transmitter unit and monitoring the received data, the receiver unit comprising user operable means for selecting one or more thresholds and being responsive to the one or more sensed parameters passing a respective user selected threshold by outputting a warning.
In a further aspect the invention provides a method of calibrating a pressure transducer for temperature-related changes in the output of the transducer, the method comprising: placing the transducer in a calibration chamber at a known temperature; varying the pressure in the chamber to a first pressure; recording data representing the output of the transducer for the first pressure; varying the pressure in the chamber to a second pressure; and recording data representing the output of the transducer for the second pressure.
The invention also provides a tyre condition monitoring system comprising at least one wheel transceiver unit mountable in a wheel of a vehicle; and a central transceiver unit for transmitting commands to the at least one wheel transceiver unit and receiving tyre condition data transmitted in reply to said commands from said wheel transceiver unit.
The invention further provides a transceiver circuit comprising an oscillator circuit for providing a reference frequency signal, a modulating circuit for modulating a data signal representing data to be transmitted with the reference signal and outputting the modulated signal for transmission, a receiver circuit for receiving a modulated data signal which receiver circuit is arranged to receive also signals from the modulating circuit derived from the reference signal, and a demodulating circuit for demodulating the received signal to extract the data therefrom.